Lateral definitions or restrictions are required to confine current and light in high performance optoelectronic devices. Processing techniques such as etching, proton implantation, regrowth, diffusion induced disordering have been developed to distribute the optical power over an array of lasing elements, leading to improved near field uniformity and increased limits on power. These approaches, however, require complex processing steps and stringent control over the epitaxial process and wafer handling.
A single-step growth process is thus highly desirable for the fabrication of index-guided lasers and laser arrays. Such devices have recently been fabricated on patterned GaAs substrates using molecular beam epitaxy (MBE) via orientation-dependent amphoteric doping of Si in AlGaAs, as disclosed by Jaeckel et al. appearing in Appl. Phys. Lett. 55, 1059 (1989), and on patterned InP substrates using metal organic chemical vapor deposition (MOCVD) via orientation-dependent dopant incorporation, as disclosed by Bhat et al. appearing in Appl. Phys. Lett. 56, 1691 (1990).
Another approach is through insertion of a current blocking layer adjacent to the quantum-well, as disclosed by Hirata et al. appearing in Appl. Phys. Lett. 58, 319 (1991).
These implementations require either a very tight control of the growth sequence or offer only limited options for the width of the waveguide.
Geometry dependent doping in crystal growth by MOCVD has been described by Bhat and Zah in U.S. Pat. No. 5,065,200 (December 1989) and in the technical paper by Bhat et al. entitled "Orientation dependence of S,Zn, . . . doping. . . : , J. Cryst. Growth 107, 772-778 (1991). The devices discussed in these publications still require selective contacting of the top layer after growth where the contact area has to line up with the ridge(s).
A laser structure reported by Narui et al. in IEEE J. Quantum Electronics 28, 4-8 (1992), entitled "A Submilliampere-Threshold Multiquantum-Well AlGaAs Laser Without Facet Coating Using Single-Step MOCVD", has the advantage of not requiring an additional photolithographic step after growth. However, this process requires careful positioning of the n-type current blocking layer in the p-cladding layer with respect to the position of the active layer. Moreover, the process requires epitaxial growth over etched substrates with high aspect-ratio, which not only demands tight control over the growth process, but also strictly limits the effective window openings for current injection on the ridges.